Centrifugal servo clutch



Jan. 20, 1953 H. B. LEWIS ET AL CENTRIFUGAL SERVO CLUTCH Filed April 5,1948 //v VENTORS. Ho WARD 5.1.5 w/s Ho WARD 1 751.0, (JR.

BY THE/R ATTORNEYS. HARRIS, K/ECH, P05 75/? & Haze/s 6v Patented Jan.20, 1953 TENT OFFICE GENTBI'FUGAL SERVQ CLUTCH Howard E. Lewis andHoward Field, J12,

Los Angeles, Calif.

Application April 3, 1949;, Serial No. 18,758

4 Claims. 1

Ourinvention relates to power transmission mechanism and moreparticularly to a clutch device for releasably connecting two rotatableelements for unitary rotation.

"It is an important object of the invention to provide aclutch devicewhich isextremely simple iirconstruction, economical to manufacture, andhighly efficient in performing its intended function.

Another object isto providea clutch device of the centrifugally-operatedtype having a driving member and centrifugally-operated clutch shoeswfloatingly mounted on the driving member and adapted to engage with theclutch surface of a drum to rotate the latter, the shoes being normally.withheld from outward radial movementby torsion springs carried by thedriving member. It is a further and important object f the invention toprovide interengaging abutmentfaces on the shoes and the driving member,these faces being so disposed that the shoes exert tangential forceswhich are in excess of the product of the outward pressure of the shoes.due to centrifugal force, against the clutch surface of the drum timesthe coefficient of friction between the clutch surface and the shoes sothat the clutch elements tend to tighten themselves into firm andpositive clutching engagement.

Another obiect is to provide a clutch device in which the clutch shoesand their torsion springs are symmetrical so that the device can beemployed for clutching together two elements for rotation in eitherdirection.

Another obiect is to provide'a clutch device in which the driving membercomprises a hub, adapted to be connected to a prime mover. and isprovided with axially-spaced plates disposed in planes normal to theaxis of the hub and between which the clutch shoes arefloatinglvpositioned and the springs are mounted. By this construction,the parts named above are adapted for as semblyas a unit without the useof screws, nuts orother similar fastening means so as to greatlysimplify thestructure and maintain its cost of manufacture at a minimum.

Further ob-iects of the invention will appear from the followingdescription and the drawing, which is intended for the purpose ofillustration only, and in which:

Fig. l is a part-sectional end View of the clutch device, the parts ofthe device being shown in inoperative position;

Fig. 2 is a cross-sectional view, taken on line 2-.-2' of Fig. 1;v

Fig. 3' is a. sectional view,v taken on line 3-3, of Fig. 1; and

' Fig. 4-is a fragmentary crossssect-ional view through the drum flangeand a clutchshoe, show ing the clutch lining applied to the shoe.

Refellingm the d in in detail. m-

proved centrifugally-operated clutch device includes a sleeve-like hub5. which is adapted to be mounted on a drive shaft 6. and to be. keyedthereto by a he i. The shaft 6. may, asa matter of convenience, beconsidered the drive shaftv of a motor or engine, indicated at 8;.inFig-2. Secured to the hub 5, as by welding; is a pair of; axially-spacedabutment plates, l0 and H; which are parallel to each other and extend;in planes normal to the axis of the hub. Held in holes 12 of the platesIt. and H are the reduced ends of spring reaction pins. 3. The platesHi. and H are substantially rectangular in outline although their endsare slightly arcuate. The plates it and i l are notched at their cornersso as to pro vide V-shaped recesses 15, one side L5 or 16' of eachrecess extending substantially radially with respect to the axis of thehub 5, and being here.- inafter referred to as an abutment face.

Adapted to be. carried by and between the plates it and H are arcuateclutch shoes l9 and 26 which have their end portions reduced in width toprovide abutmentshoulders 2| adapted to rest upon the abutment faces l6and I6. as shown in Fig. 1. The ends of the shoes I9 and zc are inclinedas indicated at. 22' to provide clearance in the manner andv for thepurpose to be later explained.

The clutch shoes I9 and are normally maintained in the inoperativeposition shown in Fig. 1, that is, with their abutment shoulders .21resting against the abutment faces t6? and I6 of the plates to and H.under the action of springs 25 and 25. The springs 25. and'26. are ofthe torsion type, each comprising a helical coil of relatively largediameter and which surrounds one of the spring-reaction pins l3. Eachspring 25. and 26 has the end portions of its coil bent out ardly inoppos te directions to provide spring arms Hand 28. The ends of the arms21' and 28 engage in apertures 29 and 36 provided at the opposite endsof the respective clutch shoes I9. and. and due to the inherentresiliency of the s rings 25. and 26. and their respective arms 21. and28', the shoes are normally held in the retracted posi-.- tionillustrated in Fig. 1. During rotation of the hub 5 and its plates I0.and II, however. the clutch shoes I 9 and 20 are subiected to corntrifugal. force which acts to move the shoes radially outward againstthe action of the sprin s :25. and 25 and into en agement with thedriven member. which is next described.

The driven member consists of a dish-shaped drum 32 which has an annularflange 33 overlying the clutch shoes l9 and, 20 to adapt the flange 9 ben by the ho s henth atter ar moved outwardly und r he uen ofcentrifugal force, so as to effect rotation of the drum. Preferably theinner surface of the ch ular flange 33, is lined with av material 35DOS-l sessing a relatively high coefficient of friction so that apositive driving action is obtained. The drum 32 i formed with orsuitably attached to a sleeve-like hub 34 which is adapted to be mountedon the end of a driven shaft 36 and keyed for rotation therewith bymeans of a key 37.

A suming that the drive shaft 6 is rotating, for example, in clockwisedirection as viewed in Fig. 1, the hub 5, plates I9 and H, springs 25and 25 and the clutch shoes 19 and 2i! will rotate therewith. At lowspeeds the springs 25 and 25 act to maintain the clutch shoes 19 and 29in their retracted position as shown in Fig. 1 so that the shoes areprevented from contacting the clutch lining 35. Consequently, no torqueis applied to the drum 32 and the latter remains stationary. As therotational speed of the driving unit 6, 5, iii, H l9 and 26 isincreased, the centrifugal force is likewise increased and eventuallythis force overcomes the torsional force of the springs 25 and 26 andcauses the clutch shoes I9 and to move radially outward into engagementwith the clutch lining 35 to apply torque thereto so as to causerotation of the drum 32 and shaft 36. As the speed of ro tation of thedrive shaft 5 is further increased, the shoes 19 and 2d are moved withgreater force against the clutch lining 35. Since the plates ii and H,springs and 2'5, and shoes !9 and 2i! are each symmetrical, the shoesare capable of applying torque to the drum 32 when the shaft 6 isrotated in either direction.

During the rotation of the shaft 5 in clockwise direction, for example,the abutment faces 18' engage the abutment shoulders 2i of the shoes isand 2t and act to push the shoes in a circular path. Due to the peculiarmounting of the shoes on the plates Ill and H, the shoes are capable ofadjusting themselves to the contour of the clutch lining and it is thusseen that a more firm and positive clutching action is produced than iseffected when centrifugally actuated shoes of the conventional pivotedtype are employed.

The present clutch device is regenerative in that the tangential forcetransmitted by the shoes is greater than the product of the outwardforce due to centrifugal force of the shoes against the clutch liningtimes the coeiiicient of friction between the shoes and lining. In otherwords, the clutch tends to tighten itself during rotation of the driveshaft 6. The magnitude of the regenerative effect may be varied byslight changes in the design of the parts. For example, moving theabutments l6 and It radially inward increases the regeneration. Changingthe abutment faces i5 and I6 from radial increases the regeneration,provided the change is in the direction which will cause the shoes topress more firmly against the clutch lining 35 and, of course, theconverse is also true. Increase of the cofiicient of friction betweenthe shoes and lining material, by changing the type of lining, alsoincreases the regeneration. By proper choice of the several factorsmentioned above, a clutch which will transmit any desired torque atpredetermined rotational speeds and release at any selected rotationalspeeds, not-greater than the predetermined rotational speeds, can bereadily designed, the release speed being, of course, lower than theengaging or driving speed. It is found that at relatively highrotational speeds, the torque transmitted by the clutch device is nearlyproportional to the square of the speed less a constant. In the range ofthe engaging speed, torque increases much more rapidly than the squareof the speed, and at very high speeds the torque approachesproportionality. Moreover, by our invention, it is possible to designthe clutch so that it has substantially the same characteristics whenits parts are worn as when new.

While Figs. 1 to 3 of the present drawing show the clutch lining 35 asapplied to the inner surface of the drum flange 33, it is within theconcept of our invention to apply it to the driving surfaces of theshoes I9 and 20, as indicated in Fig. 4, or to apply it to both thesurface of the drum flange and the shoes.

While we have herein shown and described the improved clutch device asembodied in two preferred forms of construction, by way of example, itwill be apparent that further modifications might be made in thestructure without departing from the spirit of the invention.Consequently, we do not wish to be limited in this respect, but desireto be aii'orded the full scope of the appended claims.

We claim as our invention:

1. A clutch, comprising: a rotatable driving hub provided withaxially-spaced, substantially rectangular plates fixed thereto anddisposed in planes normal to the of said hub; arcuate clutch shoeshaving reduced extensions at their ends, said extensions being slidablydisposed between said plates, said extensions providing transverseshoulders restable against edges of said plates, said shoes beingfloatable and bodily movable radially; pins extending between saidplates; a driven drum disposed coaxially with said hub and overlyingsaid shoes, said drum providing a circular clutch surface adapted to beengaged by said shoes; and torsion springs disposed between said platesand retained in place by said pins, each of said springs having its endsengageable with the opposite ends of one of said shoes to withhold saidshoes from engagement with said clutch surface uniformly throughouttheir length, said springs being adapted to yield in response tocentrifugal force of predetermined magnitude imposed on said shoesduring rotation of said driving hub, to allow outward radial movement ofsaid shoes into engagement with said clutch surface so as to effect adriving connection between said hub and said drum.

2. A clutch, including: a rotatable driving hub provided withaxially-spaced plates; arcuate clutch shoes having extensions of reducedthickness at their ends, said extensions being disposed between saidplates and the remaining portions of said shoes being disposed withoutthe space between the plates, said shoes being fioatable and bodilymovable radially, said extensions being slidable between said plates; adriven drum disposed coaxially with said driving hub and overlying saidshoes, said drum providing a circular clutch surface adapted to beengaged by said shoes; and spring means disposed between said plates andengageable with the ends of said clutch shoes and normally operative towithhold said shoes from engagement with said clutch surface, saidspring means being adapted to yield in response to centrifugal force ofpredetermined magnitude imposed on shoes during rotation of said drivinghub, to allow outward radial movement or said shoes into engagement withsaid'cluteh surface unifcrrnly throughout their lengths so as to causesaid driving hub to drive said drum.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Number Name Date Persons June 14, 1932Maurer Nov. 14, 1939 Harris Feb. 5, 1941 Harris Mar. 3, 1942 Burns June16, 1942 Norstrom et a1. June 10, 1947 FOREIGN PATENTS Country DateGreat Britain Nov. 15, 1923 Great Britain July 14, 1927 Great BritainFeb. 6, 1941 Germany June 8, 1933

